1. Field of the Invention
The present invention relates to an exposure method and an aligner, and, more particularly, to an exposure method and an aligner for exposing a substrate to a fine circuit pattern. The exposure method and the aligner find applications in the manufacture of a diversity of devices, including semiconductor chips such as Ics and LSIs, display devices such as liquid-crystal panels, detector devices such magnetic heads, and image pickup devices such as CCDs.
2. Description of the Related Art
Currently, main-stream projection aligners, which are used when devices such as Ics, LSIs, and liquid-crystal displays are manufactured through photolithographic techniques, employ excimer lasers as a light source. However, a projection aligner employing an excimer laser as its light source has difficulty forming a fine line pattern as narrow as or narrower than 0.15 xcexcm.
Theoretically, increasing the NA (numerical aperture) of an optical system or shortening the wavelength of an exposure light beam increases the line resolution. However, increasing the NA or shortening the wavelength of the exposure light is not easy, in practice. Specifically, since the depth of focus of a projection optical system is inversely proportional to the square of the NA and proportional to the wavelength xcex, increasing the NA of the projection optical system reduces the depth of focus, making focus adjustment difficult and leading to a low manufacturing yield. Further, light transmittance of most glass materials is extremely low in the far ultraviolet region. For example, even fused quartz, which is typically used at a wavelength of xcex=248 nm (in, e.g., a KrF excimer laser), drops to almost zero at a wavelength of xcex=193 nm. There is not yet available any glass material that works in a range below an exposure light wavelength of xcex=150 nm in an ordinary exposure, corresponding to a fine line pattern having a linewidth of 0.15 xcexcm or narrower.
Japanese Patent Laid-Open No. 11-143085 entitled xe2x80x9cEXPOSURE METHOD AND ALIGNERxe2x80x9d, and assigned to the same assignee as this application, discloses a high-resolution exposure method in which double exposures of two-beam interference exposure and standard exposure are performed on a substrate being exposed while a multi-value exposure on a substrate being exposed while a multi-value exposure distribution is given on the substrate being exposed at the same time. According to this disclosed method, a pattern having a minimum linewidth of 0.10 xcexcm is formed using a projection aligner and an exposure light having a wavelength of xcex=248 nm (e.g., a KrF excimer laser) and an NA of 0.6 at the image side of a projection optical system.
In the above disclosure, the two-beam interference exposure is performed using a phase shift mask (or reticle) having a linewidth of 0.1 xcexcm L and S (line and space) with a coherent light, and then the standard exposure is performed using a mask (or reticle) bearing an actual element pattern having a minimum linewidth of 0.1 xcexcm with a partially coherent light beam. In such a double exposure aligning method, two different exposure steps for two different pieces of information are required at each shot to form a single pattern. For this reason, the throughput of the aligner drops.
In a mask (or reticle) that is the original of a transfer pattern in conventional semiconductor manufacturing, the entire mask area 2, as a single area, has a single pattern (for one layer), as shown in FIG. 3, and the exposure information (e.g., exposure conditions and offsets) required to expose a substrate to the pattern is set on a per mask (reticle) basis.
To improve the throughput in a multiple-pattern aligning method, which forms a single type of pattern by exposing a substrate being exposed to a plurality of patterns at the same shot in an overlapped manner, the inventors of this invention have tried to shorten the interchange time of masks (e.g., reticles) by forming a plurality of types of patterns on a single mask (reticle).
Even when a conventional projection aligner has a plurality of areas 21 and 22 in a single mask (reticle) as shown in FIG. 4, however, there is no choice but to handle a plurality of patterns as the same pattern area using the same exposure information to complete the exposure in a single process. The conventional projection aligner thus suffers from accuracy degradation. To avoid this, the conventional projection aligner needs to process the substrate on a per area basis with the exposure information updated. In such a case, a plurality of processes needs to be performed on a single wafer, and the projection aligner suffers from accuracy degradation due to an alignment error taking place from process to process, resulting in a substantial drop in throughput due to the plurality of processes.
It is an object of the present invention to improve the throughput in a multiple-pattern aligning method which forms a single type of pattern by exposing the same shot area of a substrate being exposed to a plurality of types of patterns.
To achieve the above object, a plurality of patterns are respectively created in partitioned areas on a single original mask, and the patterns on the respective areas have different pieces of exposure information. The exposure information here includes at least one type of information from among information regarding (i) exposure conditions (e.g., an exposure setting, an exposure area, NA, "sgr" (i.e., a coherent factor of the illumination optical system), an exposure quantity, reticle transmittance, etc.), (ii) alignment conditions (e.g., an alignment illumination mode, an alignment position, an alignment mark, etc.), and (iii) offsets (e.g., alignment, focus, tilt, etc). Preferably, one of the offsets is automatically measured in the projection aligner to automatically account for it in an exposure operation.
In a preferred embodiment of the present invention, the patterns and the exposure information are appropriately switched to expose the substrate to the plurality of types of patterns in a single process. Also performed is multiple exposure, in which the same area of the substrate is exposed to the plurality of types of patterns in an overlapped manner.
According to the present invention, the exposure information is given to a plurality of types of patterns formed on a single mask (reticle), on a per pattern basis. With this arrangement, a single wafer is exposed to each pattern in accordance with appropriate exposure information, rather than being exposed to the plurality of patterns in different processes. The aligner thus enjoys substantial improvements in accuracy and throughput, as compared to a conventional aligner, which performs a plurality of exposure processes for a plurality of types of patterns.
To achieve the foregoing objects, the present invention provides, in a first aspect, an aligning method that includes the steps of partitioning an original mask into a plurality of areas in which respective areas of patterns are formed, providing respective exposure information corresponding to the patterns in different areas, on a pattern-by-pattern basis, and exposing a substrate to one type of pattern of the original mask after exposing the substrate to another type of pattern of the original mask, on the basis of the respective exposure information.
In yet another aspect, the present invention provides a device manufacturing method that includes steps of partitioning an original mask into a plurality of areas in which respective types of patterns are formed, providing respective exposure information corresponding to the patterns in different areas, on a pattern-by-pattern basis, and exposing a substrate to one type of pattern of the original mask after exposing the substrate to another type of pattern of the original mask, on the basis of the respective exposure information, to manufacture a device.